Automatic adjustment of scraper elevator using servo system having ground engaging shoe

ABSTRACT

An elevating type scraper for earth moving purposes having an open-fronted bowl with rear supporting wheels and with a scraper blade at the front of the bowl. The bowl is pivotally supported on a pair of draft members forming a part of a tractor supported draft frame. A bowl-supporting actuator is interposed between the draft frame and the front end of the bowl to determine the degree of tilt thereof and hence the depth of cut of the blade. An elevator of the endless conveyor type is positioned at the front end of the bowl having its lower end in proximity to the blade and inclined upwardly and rearwardly so that the earth loosened by the blade is conveyed into the bowl. The elevator is mounted on the bowl for upward and downward swinging movement and supported in operating position by an elevator hoist cylinder. A ground-engaging shoe is floatingly mounted with respect to the lower end of the elevator frame for riding along the ground, being movable in opposite directions from a reference position on the frame as the elevator departs from a reference position above the ground. The shoe is coupled to a servo valve on the elevator frame which is controllingly connected to the elevator hoist cylinder so that the latter is correctively actuated to maintain the elevator at a sweeping height independently of the angle of tilt of the bowl or the running depth of the blade. It is one of the features of the invention that the servo valve is bodily movable with respect to the elevator frame and positioned thereon by a separate adjusting cylinder for remote adjustment of elevator clearance.

United States Patent [191 Hyler I Sept. 9, 1975 AUTOMATIC ADJUSTNIENT OF SCRAPER ELEVATOR USING SERVO SYSTEM HAVING GROUND ENGAGING SHOE [75] Inventor: John H. Hyler, Peoria, 111.

[73] Assignee: Westinghouse Air Brake Company,

Pittsburgh, Pa.

[22] Filed: Sept. 30, 1974 [21] Appl. No.: 510,143

[52] US. Cl. 37/8; 37/DIG. 20; 172/4 [51] Int. Cl. B60P 1/36 [58] Field of Search 37/8, 89, 101; 172/4 [56] References Cited UNITED STATES PATENTS 1,707,725 4/1929 .lantz 37/8 X 2,696,287 12/1959 Foust 37/101 UX 3,512,278 5/1970 Bechman 37/8 3,513,916 5/1970 Hyler 172/4 Primary Examiner-Stephen C. Pellegrino Attorney, Agent, or FirmWolfe, Hubbard, Leydig, Voit & Osarm, Ltd.

57 ABSTRACT An elevating type scraper for earth moving purposes having an open-fronted bowl with rear supporting wheels and with a scraper blade at the front of the bowl. The bowl is pivotally supported on a pair of draft members forming a part of a tractor supported draft frame. A bowl-supporting actuator is interposed between the draft frame and the front end of the bowl to determine the degree of tilt thereof and hence the depth of cut of the blade. An elevator of the endless conveyor type is positioned at the front end of the bowl having its lower end in proximity to the blade and inclined upwardly and rearwardly so that the earth loosened by the blade is conveyed into the bowl. The elevator is mounted on the bowl for upward and downward swinging movement and supported in operating position by an elevator hoist cylinder. A groundengaging shoe is floatingly mounted with respect to the lower end of the elevator frame for riding along the ground, being movable in opposite'directions from a reference position on the frame as the elevator departs from a reference position above the ground. The shoe is coupled to a servo valve on the elevator frame which is controllingly connected to the elevator hoist cylinder so that the latter is correctively actuated to maintain the elevator at a sweeping height independently of the angle of tilt of the bowl or the running depth of the blade. It is one of the features of the invention that the servo valve is bodily movable with respect to the elevator frame and positioned thereon by a separate adjusting cylinder for remote adjustment of elevator clearance.

5 Claims, 6 Drawing Figures ffi AUTOMATIC ADJUSTNIENT OF SCRAPER ELEVATOR USING SERVO SYSTEM HAVING GROUND ENGAGING SHOE BACKGROUND OF THE INVENTION The invention relates generally to an earth moving device in the form of a tractor-drawn scraper having a blade for loosening the soil and an elevator for conveying the loosened soil into the scraper bowl, and which has improved means for maintaining the elevator in predetermined sweeping relation with respect to the ground regardless of depth of cut. In conventional elevating type scrapers the elevator is swingably mounted on the scraper bowl, with its normal running position being determined by a set of stops mounted on the scraper bowl. The stops are adjustable so as to provide the proper relationship between the conveyor and the undisturbed ground ahead of the blade for an assumed average depth of cut. However, the problem is that the depth of cut, which is under the control of the machine operator, can be varied over rather wide limits. In most prior constructions when the blade is lowered to obtain a deeper cut, the elevator is correspondingly lowered so that the elevator flights, instead of sweeping the surface of the undisturbed ground, strike the surface with some violence. Conversely when the blade is adjusted to a higher cutting level the elevator tends to ride too high, thereby reducing the loading efficiency.

Where the elevator is positioned too low, the shocks to the elevator structure and its driving system, particularly where the ground is hard, may be so severe as to be of destructive effect. As each flight strikes the ground the elevator, in effect, tries to climb up upon the flight resulting in a high peak loading, loss of power, and vibration which affects not only the elevator but the whole scraper assembly, with annoyance and fatigue to the operator.

This condition has been so consistently encountered in the past that compromises have been incorporated into the design and operation of the elevator such as driving the elevator at reduced speed and the use of ad-' ditional, more closely spaced flights, all of which have meant a sacrifice in loading efficiency. Moreover, when the elevator rides too high or too low and does not load efficiently, the loosened soil which piles up ahead of the blade must be constantly pushed by the blade requiring greater tractive effort and use of greater horsepower.

In an effort to overcome these problems, adjustable stops have been provided to accommodate the elevator height to the particular cutting level being employed, but changing of the stops is burdensome and time consuming and requires temporary shutdown of the machine. Consequently where the operator must change the cutting height frequently he usually finds it more practical to tolerate the vibration and other effects than to make frequent stop adjustments.

Moreover, conventional means for adjusting the elevator height cannot cope with extraordinary conditions such as the encountering of a straddle cut or windrow. In some applications the flights may impact the ground with such force as to be accompanied by violent up and down movement of the elevator with severe banging at the stops. Readjustment of the stops often compromises the load retention capability resulting in leakage of the soil during transport.

Efforts have been made to overcome these difficulties by imparting to the elevator a height compensation adjustment which is coordinated with adjustments imparted to the blade, so that the elevator is raised slightly when the blade is lowered and vice versa. However such compensation is referenced to the ground engaging wheels which secures satisfactory elevator adjustment over uniform terrain. But since the supporting wheels are spaced at some distance from the lower end of the elevator there is no compensation for abrupt variations in ground contour occurring right at the lower end of the elevator. In other words, the supporting wheels, as a gauging means, are not sufficiently sensitive to local abrupt variations in the undisturbed ground level.

SUMMARY OF THE INVENTION It is, accordingly, an object of the present invention to provide an automatic elevator height control for a scraper in which the elevator maintains itself in a predetermined sweeping relationship with the undisturbed ground as it exists at the bottom of the elevator. To accomplish this a ground engaging shoe is floatingly mounted with respect to the lower end of the elevator for riding along the ground surface, moving in opposite directions with respect to the elevator frame as the ground level relatively rises and falls. A servo valve on the elevator frame, connected to a source of pressure fluid, has a control element which is connected to the shoe. The servo valve controls the flow of fluid at the opposite ends of the elevator hoist cylinder so that the latter is correctively actuated to maintain the shoe in an equilibrium position with respect to the elevator with the result that the elevator is maintained in a predetermined sweeping relation with the ground independently of the degree of tilt of the bowl and independently of the cutting level of the blade. Means are provided for adjusting the servo valve thereby to adjust the precise sweeping height maintained by the elevator.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a complete elevating scraper assembly, including tractor.

FIG. 2 is a fragmentary side view of an elevator showing the flights in desired sweeping clearance relationship with respect to the ground.

FIG. 3 is a diagram showing the lower end of the elevator frame and the linkage associated with the ground engaging shoe.

FIG. 4 is a schematic diagram of the hydraulic servo system.

FIG. 5 is a schematic diagram of an hydraulic circuit providing alternate modes of operation.

FIG. 6 is a diagrammatic front view showing use of a separate sensor at each side of the elevator.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings there is disclosed a scraper assembly made up of a bowl 10 having a frame 11 and a tractor 12 having a draft frame 13. The draft frame includes a so-called gooseneck 14 which is of rigid construction pivoted to the tractor at 15 for horizontal swinging movement and carrying a transversely extending torque tube 16 to which draft members 17 are secured. The latter extend rearwardly and downwardly and are pivoted at 18 to the respective sides of the bowl. The rear end of the bowl is supported upon a pair of wheels 19.

Mounted along the front edge of the bowl is a blade which digs into the ground to a depth determined by the angle of tilt of the bowl about the draft axis 18. For determining this angle, and cutting depth, a bowl supporting actuator 21 is provided at each side of the bowl, the actuator shown in FIG. 1 having an upper point of anchoring 22 to the draft frame and a lower connection 23 to the front portion of the bowl structure. For the purpose of conveying the soil loosened by the blade to the back of the bowl, an elevator is provided (see especially FIG. 2) having a lower end which rides above and slightly ahead of the blade 20 and which extends rearwardly and upwardly enclosing the front end of the bowl. The elevator includes a pair of longitudinal frame members 31 journalling a cross shaft 32 driving a pair of sprocket wheels 33. At the bottom end of the elevator, in alined positions, are idler wheels 34. Trained about the sprockets and idlers are conveyor chains 35 having transversely extending flights 36. The drive shaft 32 is driven by a motor 37 through a gear box 38.

The blade moving through the ground tends to break the soil clear along a shear plane indicated at 40. The elevator is mounted so that its low point, with respect to the undisturbed ground surface 41, approximately coincides with the end 42 of the shear plane. The elevator should be sufficiently elevated above the ground under running conditions as to provide a slight amount of sweeping or grazing clearance dl which may, for example, be on the order of an inch or even a fraction of an inch. For the purpose of mounting the elevator for upward and forward swinging movement, thereby to change the position of the elevator with respect to the ground, and also for permitting the elevator to yield upon encountering boulders or other obstructions, the frame of the elevator is swingably supported upon a pair of arms 44 which are pivoted to the bowl structure along a transverse axis 45. Clearance is referred to the flight envelope 43. In conventional constructions, to determine the height at which the elevator rides for a given depth of cut, limit stops are used which may be mounted upon the bowl structure, on opposite sides thereof, in the downward path of swing of the frame members 31, with shims being adjustably interposed to vary the height at which bottoming occurs. However in accordance with the present invention the elevator, rather than being supported upon stops, is supported by an elevator hoist cylinder under the control of a servo valve which is coupled to a ground-engaging shoe. Referring especially to FIG. 3 the elevator hoist cylinder, indicated at 50, has an upper point of connection 51 to the supporting structure and a lower point of connection 52 to a frame plate 53 which is secured to the longitudinal frame member 31 of the elevator. As set forth in FIG. 4 the hoist cylinder 50 is hydraulically connected to a servo valve 60 which has a body 61 fitted with a slidable plunger 62 and having an anchoring point 63. Pressure and sump connections are provided at P and S respectively.

For operating the servo valve a ground-engaging shoe 70 is provided which is in the form of a lever bent into arcuate shape having a fulcrum 71 and an output connection 72. To provide pivot connections at points 71, 72 a plate or bracket 73 forms an integral extension of the shoe. For the purpose of limiting the angel of swing of the shoe the end of the shoe is inwardly bent as indicated at 75, with stops 76, 77, which are secured to the elevator frame, being interposed in the path of downward and upward movement. The output connection 72 of the shoe is connected to the valve plunger 62 by means of a link 78.

When the elevator is riding with the flight envelope 43 at the desired sweeping distance d1 above the undisturbed ground level 41, the servo valve is in the condition illustrated in FIG. 4 and the elevator hoist cylinder 50 is in its equilibrium condition blocked against movement in either direction. For the purpose of enabling precise remote adjustment of the grazing clearance, servo valve body 61, instead of being'fixed to the elevator frame member 31, is coupled to it by means of an adjusting cylinder 80, one end 81 of which is connected to the valve body while the other end 82 is anchored to the elevator frame. Any convenient type of fluid supply device, generally indicated as a valve V, connected to the pressure and sump lines P, S may be used to control the degree of elongation of the cylinder, that is, the cylinder control point, and hence the clearance which exists between the elevator flights and ground when the valve 60 is in its neutral condition.

It will be apparent, however, that the invention is not limited to use of an adjusting cylinder and that any convenient mechanical adjustment may be substituted effective to change the spacing between the end 63 of the valve and the anchoring point 82 on the elevator frame.

In reviewing the operation of the construction described above, it will be assumed that the system is in the condition illustrated in FIG. 4, that is, with the scraper in motion, the ground sensing shoe riding along the undisturbed ground surface 41 and with the flight envelope 43 at the predetermined sweeping height dl.

Let it be assumed that the operator desires to take a deeper cut, operating a control valve (not shown) so that the bowl supporting cylinder 21 elongates, accompanied by downward tilting of the bowl and blade and lowering of the elevator frame. Such lowering of the elevator frame occurs for two reasons; in the first place the axis of attachment 45 of the elevator to the bowl structure is lowered and, in addition, there is a slight drop in the level of the torque tube 16 causing the elevator hoist cylinder to be bodily lowered. The lowering tendency of the elevator toward the ground results in the relatively upward rookering, or scissoring, movement of the sensing shoe in a clockwise direction pulling the valve plunger 62 to the right as viewed in FIG. 4 and connecting the hoist cylinder 50 to the pressure and sump lines in a direction to contract the cylinder. Such contraction raises the elevator frame away from the shoe which remains in ground engagement, restoring the shoe to its initial reference condition with respect to the elevator frame and restoring the valve 60 to neutral so that fluid flow to the hoist cylinder is cut off, maintaining the elevator in its new position.

The converse occurs when the operator sets the blade for a shallower cut. This tends to raise the elevator causing relative dropping movement of the shoe with respect to the elevator frame, moving the valve plunger 62 in the opposite direction, that is, inwardly, resulting in expanding movement of the cylinder 50 and thereby restoring the elevator to its desired sweeping condition with respect to the undisturbed ground level.

It is one of the features of the present system that it enables the elevator to cope with any abrupt irregularities in ground level. Suppose, for example, that the scraper should encounter a windrow of soil extending parallel to the direction of scraper movement. Absent the present invention the elevator would continue to ride at its original level and the elevator flights would strike the dirt of the windrow with a severe impact and with the reacti n force causing the elevator frame to spring upwardly, followed a moment later by the dropping of the elevator frame against the bottoming stops as the windrow is passed. Even relatively sophisticated elevator height controls dependent upon the supporting wheels as a reference would not detect the presence of obstructions of this type because of the abrupt and localized nature. However, since the ground sensing shoe projects forwardly ahead of the flight envelope 43,

the shoe" is immediately rocked upwardly relative to the elevator frame, retracting the plunger 62 of the valve 60, causing fluid to be fed to the hoist cylinder 50 to raise the elevator frame thereby to prevent downward impact of the flights against the windrow. In short, self protecting upward movement of the elevator frame is achieved without necessity for the frame to climb up upon the elevator flights as in the usual selfprotection mode.

Similarly where the elevator encounters a shallow transversely extending ditch, the dropping of the shoe into the ditch accompanied by inward movement of the valve plunger elongates the hoist cylinder 50 so that the elevator tends to follow the ditch contour. It will be un derstood that the usual limit stops are provided between the elevator frame and the bowl so that under such conditions the catenary of the elevator is kept safely clear of the blade.

While the invention has been described thus far in connection with a single sensing shoe, single servo valve and single hoist cylinder, it will be understood that sensing shoes 70 may be provided on each side of the elevator structure spaced closely to the elevator flights as shown in FIG. 6 and with each shoe having its individually controlled servo valve 60 and cylinder 50. Where dual cylinders 50 are used lost motion may be provided in the piston rod connection as indicated at 52a in FIG. 3 so that the cylinders, which may receive contrary instructions from their ground-engaging shoes 70, will not strain against one another. With the lost motion, the more contracted one of the two cylinders will always prevail to keep the elevator at a safe height.

In accordance with one of the aspects of the present invention, the servo-actuator 50 which supports the elevator, in addition to its servo function, is utilized for manual raising and lowering of the elevator and to establish conditions referred to as float and checked float. To achieve this versatility I prefer to use an hydraulic circuit set forth at 90 in FIG. 5 including an auto manual selector valve 91 and a manualfloat selector valve 92. The auto-manual valve 91 is shown in its manual position. The circuit includes, in addition, a checked float and free float selector valve 93, the latter being shown in its normal or free float condition.

In the free float condition the actuator 50 is effectively by-passed by a fluid loop so that it does not have any control upon elevation. However, the fluid loop includes a damping orifice 95 so that the actuator serves, in this mode, as a shock absorber. To achieve the checked float mode the actuator, instead of being simply bypassed, is effectively shunted by a check valve 96 so that, upon striking a windrow or other obstruction, the actuator 50 is free to accommodate the rising elevator movement but, because of the checking action, will hold the elevator in its upraised position until such time as the elevator may be released. Thus where the scraper encounters a windrow, the elevator, after attaining windrow height, will remain at such height until the operator by manipulation of the valves takes over control or restores the elevator to automatic control. Thus, the operator, after shifting the valve 3 to normal, may either resume automatic level control by movement of the valve 91 to its auto position or manually control the elevator or obtain free float by manipulation of valve 92.

To review the functions obtainable in the hydraulic circuit of FIG. 5, it will be assumed, first of all, that the valve 91 is in its auto position and that valve 93 is in its normal (illustrated) position. Automatic elevator clearance will then be achieved as discussed in connection with the earlier figures.

Upon encountering a windrow, the operation will be determined by the width and direction of the windrow. If the windrow is wide or transversely extending, automatic elevation will occur as described, but if the windrow is narrow and straddled, and therefore not detected by the sensing shoes, the operator may move valve 91 to its manual condition, valve 92 to float and valve 93 to checked float so that the elevator, after rising to a new height, will maintain such height until the obstruction is safely passed.

While the invention has been described in connection with the elevator hoist cylinder 50 coupled to the tractor draft frame 13, it will be understood that the invention is not limited to such connection and that the upper end of the cylinder 50 may, if desired, be connected directly to the bowl structure. It is true that these two points of connection undergo different amounts of change in level for each unit of change in level of the blade, but it is one of the features of the present invention that the elevator level is immune to its mode of support and, during automatic operation, controlled solely in accordance with information sensed by the ground engaging shoes.

Although it is one of the features of the present construction that no fixed but adjustable stops are necessary to establish elevator running height, it is desirable to have a pair of bottoming stops to determine the ultimate condition of proximity between the elevator and the bowl to keep the elevator flight envelope safely clear of the blade, especially during transport. Such bottoming stops may include a first stop 101 on the bowl and a second, cooperating, stop 102 on the elevator frame (see especially FIG. 2).

It will be apparent that the objects of the invention -are amply carried out by the disclosed height- In a conventional scraper adjustable working" stops (as contrasted with limit stops), interposed between the elevator frame and the bowl, are relied upon to maintain the elevator at a predetermined level with respect to the blade, set on the assumption that there is to be a certain depth of cut. The presence of working stops compromises load retention since the elevator is prevented from closing against the load during transport. By contrast, in the present device, raising the bowl for transport causes the sensing shoe 70 to drop which instructs the valve 60 to elongate the actuator 50 which permits the elevator to settle into a soil-retaining position limited only by contact between the limit stops 101, 102. Even during normal operation retention is favorable since the elevator operates constantly at its lowest position, consistent with maintenance of ground clearance. When the operator of a conventional scraper sets the fixed elevator stop for a certain depth but thereafter, by raising the bowl, cuts at a shallower depth, the result may be the raising of the elevator so high that it can neither efficiently elevate, nor efficiently retain, the scraped soil.

Not only does the present elevator adjusting system permit the elevator to operate in low position with respect to the bowl automatically upon taking of a shallow cut, but it enables the elevator, by its combination of upward and forward swing, upon taking of a deeper cut, to move forwardly so that the lowermost point of the flight envelope is constantly maintained at its most efficient position, namely, at the region of emergence of the earth shear plane, in other words, at the junction between the disturbed and non-disturbed earth, regardless of depth of cut. Subsequently, when the bowl is raised for transport, the elevator frame, unimpeded by adjustable stops, may drop downwardly into limit-stop engagement, that is, to a level in which reliable soil retention is assured. I

Because of the ability of the elevator to independently follow the ground contour, with the elevator being smoothly raised and lowered by servo action, the violent up and down movements usually experienced as a flight engages undisturbed ground are eliminated. Thus in determining the flight spacing and speed there is no longer any need to compromise efficiency with risk of self-destruction. Relatively widely spaced flights may be operated at high speed with elevating efficiency only in mind and with no need to consider conditions of impact. By designing the elevator for greatest elevating efficiency it is possible to handle a broad range of soils and to make use of the maximum earth moving capability of the bowl and scraper blade structure.

One of the further advantages of using a servo system for automatic elevator positioning is that there is no need to use auxiliary energy-absorbing stops to cushion movement at the ends of the stroke. The fluid in the system provides a certain amount of inherent damping action so that there is no uncontrolled release of energy, and it will be apparent to one skilled in the art that additional damping may be readily incorporated by adjusting orifice size in the path of fluid flow.

Not only does the servo system permit continuous, prompt and automatic adjustment of elevator height under normal digging conditions but alternate modes of operation are available, particularly the free float and checked float modes with minimum complication and at minor expense. In the free float mode the elevator may move freely along its path within the limits of cylinder stroke, yet employ hydraulic energy absorption to handle high dynamic loads at the extremes of cylinder stroke, as previously touched upon. When the system is operated in the checked float mode the elevator is free to move upward until the end of the cylinder stroke is reached, but is checked against any downward movement. Accordingly, in a straddle cut or windrow loading operation, where the shoe establishes minimum elevator clearance above the ground, and where the flights may contact the straddle cut or windrow surface, the system may be operated so that the elevator may raise itself to an alternate height from ground level which can be maintained for that loading path, following which normal operation may be restored.

Since the hydraulic valving permits manual override, it will be apparent that the elevator may be raised at will as necessary to accommodate boulders or other obstructions which might otherwise damage the elevator structure. Aside from this, the machine operator may rely upon the essentially automatic operation of the system and may devote his attention to more important concerns such as steering and adjustment of depth of cut.

What is claimed is:

1. In an elevating type scraper for earth moving purposes, the combination comprising an open-fronted bowl having sides, back wall and a floor, ground wheels for supporting the bowl and mounted behind the back wall, a scraper blade extending along the front edge of the floor, a tractor-supported draft frame, a pair of draft members pivotally secured at the rear ends to the sides of the bowl and extending forwardly and up wardly having rigid connection at their front ends to the draft frame, means including an actuator interposed between the draft frame and the front end of the bowl and having control means for determining the degree of tilt of the bowl about its supporting wheels and hence the depth of cut of the blade, an elevator positioned at the open front end of the bowl, the elevator having a frame which extends upwardly and rearwardly from the region of the blade and which is pivoted to the bowl for swinging movement about a transverse axis, the elevator having a pair of endless chains with transversely arranged flights, the chains having means for driving at the upper end of the frame and trained about rollers at the lower end so that the flights sweep the soil loosened by the blade backwardly into the bowl, means including an elevator hoist cylinder for supporting the elevator with respect to the ground, a ground engaging shoe floatingly mounted with respect to the lower end of the elevator frame for riding along the ground and movable in opposite directions from a reference position on the elevator frame as the elevator departs from a reference position above the ground, a servo valve on the elevator frame having a source of pressure fluid and a control element connected to the shoe, the servo valve being controllingly coupled to the elevator hoist cylinder so that the latter is correctively actuated to maintain the elevator at a desired sweeping height independently of the angle of tilt of the bowl, and means coupled to the servo valve for adjusting the maintained sweeping height.

2. The combination as claimed in claim 1 in which the shoe is in the form of a lever of arcuate shape extending forwardly of the envelope of the flights and pivoted adjacent its forward end to the leading edge of the elevator frame for vertical swinging movement, and in which stops are provided on the elevator frame for limiting the range of swinging movement.

3. The combination as claimed in claim 1 in which means are provided for adjustingly positioning the servo valve on the elevator frame to adjust the maintained running clearance of the elevator with respect to the ground.

4. The combination as claimed in claim 3 in which a pair of hoist cylinders are provided connected to respective sides of the elevator frame and in which a pair of ground engaging shoes are floatingly mounted on the sides of the elevator frame in close straddling relation to the transversely extending flights, with the shoes being individually connected to servo valves for respective automatic actuation of the elevator hoist cylinders.

5. The combination as claimed in claim 1 in which cooperating bottoming steps are provided on the elevator frame and on the bowl for limiting the downward swing of the elevator toward the bowl to an amount required to prevent physical contact between the flights and the scraper blade while maximizing confinement of the soil collected in the bowl when the bowl is tilted upwardly out of ground engagement under transport conditions. 

1. In an elevating type scraper for earth moving purposes, the combination comprising an open-fronted bowl having sides, back wall and a floor, ground wheels for supporting the bowl and mounted behind the back wall, a scraper blade extending along the front edge of the floor, a tractor-supported draft frame, a pair of draft members pivotally secured at the rear ends to the sides of the bowl and extending forwardly and upwardly having rigid connection at their front ends to the draft frame, means includinG an actuator interposed between the draft frame and the front end of the bowl and having control means for determining the degree of tilt of the bowl about its supporting wheels and hence the depth of cut of the blade, an elevator positioned at the open front end of the bowl, the elevator having a frame which extends upwardly and rearwardly from the region of the blade and which is pivoted to the bowl for swinging movement about a transverse axis, the elevator having a pair of endless chains with transversely arranged flights, the chains having means for driving at the upper end of the frame and trained about rollers at the lower end so that the flights sweep the soil loosened by the blade backwardly into the bowl, means including an elevator hoist cylinder for supporting the elevator with respect to the ground, a ground engaging shoe floatingly mounted with respect to the lower end of the elevator frame for riding along the ground and movable in opposite directions from a reference position on the elevator frame as the elevator departs from a reference position above the ground, a servo valve on the elevator frame having a source of pressure fluid and a control element connected to the shoe, the servo valve being controllingly coupled to the elevator hoist cylinder so that the latter is correctively actuated to maintain the elevator at a desired sweeping height independently of the angle of tilt of the bowl, and means coupled to the servo valve for adjusting the maintained sweeping height.
 2. The combination as claimed in claim 1 in which the shoe is in the form of a lever of arcuate shape extending forwardly of the envelope of the flights and pivoted adjacent its forward end to the leading edge of the elevator frame for vertical swinging movement, and in which stops are provided on the elevator frame for limiting the range of swinging movement.
 3. The combination as claimed in claim 1 in which means are provided for adjustingly positioning the servo valve on the elevator frame to adjust the maintained running clearance of the elevator with respect to the ground.
 4. The combination as claimed in claim 3 in which a pair of hoist cylinders are provided connected to respective sides of the elevator frame and in which a pair of ground engaging shoes are floatingly mounted on the sides of the elevator frame in close straddling relation to the transversely extending flights, with the shoes being individually connected to servo valves for respective automatic actuation of the elevator hoist cylinders.
 5. The combination as claimed in claim 1 in which cooperating bottoming steps are provided on the elevator frame and on the bowl for limiting the downward swing of the elevator toward the bowl to an amount required to prevent physical contact between the flights and the scraper blade while maximizing confinement of the soil collected in the bowl when the bowl is tilted upwardly out of ground engagement under transport conditions. 